meta: quoted frontmatter scalars containing ": " are silently dropped

[drawmeanelephant]

Summary

oliver meta silently drops any frontmatter key whose value is a quoted scalar containing ": " (colon followed by a space). The key simply never appears in the JSON output — no warning, no error. Downstream templates then render an empty $title$ / $description$ with no signal that anything went wrong.

Found from Rotkeeper (rendering pipeline pins commit 06dd6403c505b4863a54c548c978e494b55eb759): every scaffolder-generated showcase page titled "Showcase: <name>" rendered an empty <title> and header.

Reproduction

$ printf -- '---\ntitle: "No Colon Here"\ndescription: "d"\n---\n\nx\n' > t1.md
$ printf -- '---\ntitle: "Has: Colon"\ndescription: "d"\n---\n\nx\n' > t2.md
$ oliver meta --from markdown --format json < t1.md | jq -r .title
No Colon Here
$ oliver meta --from markdown --format json < t2.md | jq -r .title
        # <- empty; key absent from the JSON entirely

Characterization

Input	Result
title: "Has: Colon"	key dropped
description: "Desc: here" and author: "A: B" (same doc)	all three keys dropped — not title-specific, every quoted scalar with ": " is affected
title: 'Single: Colon' (single quotes)	key dropped
title: "NoSpace:Colon"	parsed correctly
title: "Trailing: " (colon+space at end of scalar)	key dropped
title: Unquoted: Colon Value	key dropped — arguably expected, that's ambiguous YAML

So the trigger is specifically the ": " sequence inside a quoted scalar.

Expected behavior

Quoted YAML scalars may legally contain ": "; the parser should keep the key and expose the full string in meta output. At minimum it should emit a loud warning rather than silently omitting the field — silent empty titles are painful to debug downstream (we only caught it because a cross-template rendering audit diffed <title> contents).

Environment

• Pin: 06dd6403c505b4863a54c548c978e494b55eb759 (rolling builds release)
• Command: oliver meta --from markdown --format json
• Discovered via Cross-theme rendering pass for docs, books, reports, indexes rotkeeper#260; fixed on our side by generating colon-free titles (Quality pass: a11y gate, theme families, cross-theme rendering (#258, #253, #260) rotkeeper#275), but users authoring their own frontmatter will hit this constantly.

[drawmeanelephant]

Verified fixed on main at f1fbb1c (includes #121 b830475 → c91db48).

Root cause was src/meta.zig classifying : / # before quote decoding, so quoted scalars like title: "Has: Colon" projected as "" (src/meta.zig:108, src/frontmatter.zig:420). Fix moves isOutOfSubsetScalar inside decodeScalar after decodeDoubleQuoted/decodeSingleQuoted (src/meta.zig:316,343,373), mirroring src/frontmatter.zig:434.

Verification (oliver 1.0.0, zig build test --summary all 455/455):

• title: "Has: Colon" → Has: Colon (was "")
• description: "Desc: here" + author: "A: B" → all three kept
• title: 'Single: Colon', "NoSpace:Colon", "Trailing: " → all kept
• bare Unquoted: Colon → "" (expected)
  Pins: src/meta.zig:495, src/frontmatter.zig:757.

PR #124 opened as verification closure (empty commit on top of main). Closing as completed.